The invention relates to a roller with an eddy current brake.
Such a roller is known from EP 1 243 528 A1, said roller having a brake device in the form of an eddy current brake in the interior of an outer tube. To this end, the outer tube, i.e. the roller shell, is formed with an insert body of electrically conductive material, such as copper or aluminium, on the inner surface thereof. The roller shell is rotatably supported on a rod, which is fixed in a stationary frame. Fixedly arranged permanent magnets with poles are arranged on the rod, which are located at a distance of an air gap to the insert body. In the case of a rotation of the roller shell together with the insert body relative to the stationary poles, eddy currents are induced in the insert body by the magnetic field, said currents opposing braking torque to the rotational movement of the roller shell, which increases as the speed increases.
To this, hereinafter referred to as the first braking torque, a second braking torque is added when the magnetic field also causes eddy currents in the roller shell that is made of electrically conductive, non-magnetizable material, such as aluminum or stainless steel. If the roll shell is further made of magnetizable material, such as steel, there is a further effect of the magnetic field on the roller shell due to its rotation about the stationary magnetic field to a constant remagnitization, whereby a third braking torque occurs.
Such a roller is used on a roller conveyor, which is equipped with a plurality of rollers without any braking device and extends with a slightly inclined conveyor path. Conveyed goods, which are placed thereon, are conveyed without any further drive by the downhill-slope force caused by the dead weight. During the operation of such roller conveyors, the conveyed goods may come to a standstill for various reasons, so that the conveyed goods pile up without free space between individual conveyed articles. As soon as the further transport of the conveyed goods starts again, it is required that the conveyed goods automatically start to move again on the inclined conveyor path. The explained situation involves the difficulty of, on the one hand, achieving automatic rolling-off of the conveyed goods on the roller conveyor by means of the inclined conveyor path, and, on the other hand, avoiding that the conveyed goods assumes an inappropriate greater speed. To control the speed of conveyed goods, it is known to use rollers with integrated brakes of mechanical or electrical type, similar to an electric motor, or as eddy current brakes at suitable positions in the roller conveyor.
When the known roller with an eddy current brake is used, it must be taken into account that an automatic movement of previously stopped conveyed goods can only be achieved by accepting a greater inclination of the conveyor path, from which, in turn, greater energy must be absorbed when conveyed goods pile up.
DE 28 21 973 A1 discloses a magnetic torque coupling in which eddy currents as a result of relative movements of stationary permanent magnets to an eddy current support and also remagnitization of components are used for a desired torque transmission. The document is only of interest with regard to the cup-shaped coupling parts.
With regard to the prior art on permanent magnets, magnetism, and eddy current brakes, reference is made to the textbook “Europa-Lehrmittel, ELEKTRONIK, 1. Teil: Grundlagen-Elektronik 3. Auflage”, pages 73 to 75 and pages 96 and 97.